1. Field of the Invention
The present invention relates to disk drives and more specifically, to a disk clamp for a disk drive that provides a uniform clamping load.
2. Description of Related Art
Work stations, personal computers and laptop computers require disk drives that provide a large amount of data storage within a minimal physical area. A disk drive typically includes one or more hard disks that are rotated at a constant high speed by a spindle motor. Generally, disk drives operate by positioning a transducer or read/write head over respective tracks on the disks. The information is written to and read from tracks on the disks through the use of an actuator assembly which rotates during a seek operation. The actuator is coupled to control electronics which control the positioning of the actuator and the read/write functions of the transducer. A typical actuator assembly includes a plurality of actuator arms which extend towards the disks with one or more flexures extending from each of the actuator arms. Mounted at the distal ends of each of the flexures is a head which acts as an air bearing enabling the head to fly in close proximity above the corresponding surface of the associated disk. The demand for increasing density of information stored on these disks is becoming greater and greater for a multitude of reasons. The increase of multi-user and multi-tasking operating system work stations which provide an operating environment requiring the transfer of large amounts of data to or from the hard disks, large application programs, the popularity of notebook and laptop computers and the continuing trend toward higher performance microprocessors all contribute to this end. The structural design of these systems is also continually shrinking, requiring hard disk drives having high capacity storage capability while occupying a minimal amount of space within the system.
In order to accommodate these demands, there is a need for smaller hard disk drives which have increased storage capacity. To read this more densely stored information, engineers have decreased the gap fly height between the heads and the disks. Reducing the gap fly height leads to increased contact between a head and the data portion of the disk during operation of the disk drive. Nevertheless, there has been an industry wide push to reduce the height at which transducers are maintained over the disk surface without actually contacting the disk surface.
When a transducer flies over a rotating disk, the flying height tends to fluctuate slightly above and below a normal flying height because the disk surface itself is not flat. At lower flying heights the variation in the fly height may cause the transducer to contact the disk surface. This intermittent contact, if repeated, can damage the transducer or the disk and may cause drive failures.
In conventional disk drives, a stack of disks is provided on a cylindrical hub of a spindle motor. A disk clamp is provided on top of the stack of disks on the hub. The clamp has a larger radius than that of the hub so that the outer diameter of the clamp is in contact with the top disk. A plurality of screws, or a single screw, fit through holes located in the disk clamp. These screws (screw) are threaded into bores in the hub. When a screw is tightened, the force applied to the midsection of the disk clamp is transferred to the outer circumference of the disk clamp which contacts the disk surface. This force secures the disks to the spindle motor hub. The disks must be secured under considerable force in order to prevent any slippage of one or more disks in the presence of mechanical shocks. Even very slight slippage of a disk within a drive could result in mechanical misalignment of the transducer which could result in data transfer errors or failure.
Disk clamp design is quite critical in high performance disk drives. Ideally, the disk clamp provides a uniform clamping force along its clamping surface to avoid disk distortion. The disk clamp must be designed to reduce overall clamp force variation. Minimizing height variations resulting from component tolerance and differential thermal expansion will result in less total clamp force variation.
Spindle motor assemblies often utilize a rotating spindle hub journaled to a non-rotatable spindle shaft. A disk clamp is typically secured to the rotating spindle hub to exert a downward axial force on the mounted disks and disk spacers. Typically, the disk clamp exerts the downward force through a series of radially positioned screws torqued into the spindle hub. The radial positioning of the screws exerts a clamping force on the spindle at the periphery of the disk clamp in closer proximity to the mounted information storage disks and disk spacers. The positioning of the screws in the disk clamp causes the downward force to be exerted in a non-uniform manner. Non-uniform clamping force causes variations in the load force and as a result, causes, at least the top mounted information storage disk to be physically distorted. Distortion of the top disk even by as little as 40 microinches can lead to operational errors during recording and reproduction of data on the information storage disk.
In a second type of spindle motor assembly, the spindle shaft and spindle hub portion both rotate about a bearing sleeve. In this arrangement a single screw is used to secure the disk clamp to the rotating spindle shaft. In order to develop a clamping force with a single screw similar to the force developed by a plurality of screws surrounding the non-rotatable shaft, it is necessary to apply a much higher torque to the single screw. This relative high torque leads to a number of problems, including over-stressing the spindle shaft bearing. These high torque related problems can damage the bearing and lead to failure of the spindle motor.
In spite of previous attempts, there is still a need to overcome the shortcomings of the traditional single screw disk drive spindle motor assembly as well as the multiple screw spindle shaft spindle motor assembly by providing a disk clamp that produces a uniform clamping load on the storage disks supported by the hub of the spindle motor.